A semi-aromatic polyamide, which is a polycondensation product of an aliphatic diamine and phthalic acid, is excellent in various performances including heat resistance, as compared with an aliphatic polyamide. Accordingly, developments for the use of semi-aromatic polyamides in applications to films and molded products have recently been promoted. For example, JP09-012714A describes, as a semi-aromatic polyamide, nylon 9T including as constituent components an aliphatic diamine having 9 carbon atoms and terephthalic acid. Nylon 9T has a high melting point falling in the vicinity of 300° C., and hence is high in heat resistance and comparatively low in water absorbability, and accordingly hardly undergoes dimensional change due to water absorption. Accordingly, the use of nylon 9T in various industrial applications has been attracting attention.
Nylon 9T has such properties as described above, and hence it is possible for the film of nylon 9T to establish the compatibility between the heat resistance and the dimensional stability, in contrast to the fact that it has been difficult for conventional thermoplastic films to establish such compatibility. Accordingly, the development of nylon 9T as the material for films has been actively pursued. In particular, it is expected to apply the film obtained from nylon 9T to the fields of so-called industrial films such electric and electronic components and optical films.
Such applications often include applications requiring deformation resistance including flexibility, flex resistance and keying durability, namely, applications to board films and cover lay films for flexible printed circuits (FPCs), and insulating films for switches and touch panels. In particular, in the case where a high-temperature heat treatment step such as reflow treatment is required at the time of processing as in the applications to FPCs, the deformation resistance after performing the heat treatment is demanded.
However, the films formed of nylon 9T are high in the modulus of elasticity at room temperature, and hence sometimes insufficient in the foregoing resistance against deformation. Moreover, the high-temperature heat treatment unfortunately degrades the deformation resistance of the films formed of nylon 9T.
JP2004-217698A discloses a resin composition prepared by adding to a polyamide an elastomer and a cross-linking agent. The resin composition can acquire oil resistance, heat resistance, gas barrier property and flexibility by dispersing the elastomer in the polyamide. The resin composition can acquire thermoplasticity by dispersing in the polyamide the elastomer formed to have a fine spherical shape of approximately 0.1 to 30 μm in diameter, and thus can undergo general-purpose heat melt molding such as extrusion molding, injection molding or press molding. In the first place, the improvement of the impact resistance by finely dispersing an elastomer in the polyamide has been heretofore known as an incompatible polymer alloy technique. On the other hand, it is also heretofore known that different morphologies such as dispersion state of an elastomer result in significantly different properties of molded articles. Accordingly, it is difficult to apply the technique described in JP2004-217698A to the method for producing a thin stretched film wherein the production method is completely different in processing method from heat melt molding, involves deformation at the time of processing and enhances anisotropy in the deformation direction. It is much less possible for the technique described in JP2004-217698A to solve the above-described problem that heretofore known films formed of nylon 9T are insufficient in deformation resistance and are not satisfactory in the deformation resistance after performing heat treatment.